基于弹光调制的高灵敏旋光测量

为了实现连续稳定、高速、高精度和高灵敏度的光学旋光测量, 考虑到弹光偏振调制技术具有高的调制频率、调制纯度、调制精度和良好的调制稳定度等应用优势, 设计了一种基于弹光调制的旋光测量新方案. 检测激光经起偏器、测量样品、弹光调制器和检偏器到探测器的光路设计, 使得测量系统选用较少的光学器件, 最大化地降低了光学器件可能引入的测量误差; 起偏器和检偏器偏振轴相对于弹光调制器快轴方向分别取0°和45°的光学安排, 并选择弹光调制的二倍频信号作为研究对象, 有效避免了弹光调制器剩余双折射对旋光样品测量的影响, 提高了旋光测量精确度; 将探测器输出调制信号的直流和交流分开输出, 并将交流信号进行前置放大处理, 然后再锁相输出, 进一步提高了测量灵敏度. 设计了将激光调制为圆偏光, 然后精确调节起偏器来替代样品的旋光测量验证试验, 确定了系统旋光测量的比列系数, 并且获得旋光测量灵敏度为3.15×10^-7 rad, 测量精度优于0.3%. 所以, 本方案实现了较高灵敏度旋光测量, 有望应用于高灵敏旋光测量领域, 并且本方案的实验可为高灵敏旋光测量系统的定标提供参考.

High sensitive measurement of optical rotation based on photo-elastic modulation

In order to realize the continuous and stable, high speed, high precise and high sensitive measurement of optical rotation, and considering the application advantages of photo-elastic polarization modulation technology with high modulation frequency, high modulation purity, high modulation accuracy and good modulation stability, a new scheme about the measurement of optical rotation based on photo-elastic modulation is presented. Probe laser orderly passes through a polarizer, the rotation sample to be measured, a photo-elastic modulator, and a analyzer, and finally reaches the detector, this system uses less optical devices than any others previously reported, so it considerably reduces the measurement error that may be introduced by the optical devices. In the detecting of light path, the polarization axes of the polarizer and analyzer are respectively adjusted with respect to the photo-elastic modulator's fast axis directions 0° and 45°, the optical arrangements make the rotation angle to be measured appear in the alternating current signal, and the photo-elastic modulator's residual birefringence only appears in the odd harmonics. Consequently, the second harmonic signal of photo-elastic modulation is selected as the object to study, which effectively avoids the influence of residual birefringence of the photo-elastic modulator on optical rotation measurement, and efficiently improves the accuracy of optical rotation measurement. What is more, the detector output signal is separated into two parts, the direct current and alternating current signal. The alternating current signal is amplified, then outputs by a lock-in amplifier, which enhances the measurement sensitivity further. A ingenious verification test experiment is done, firstly, the probe laser is modulated into circularly polarized light, and then precisely rotates the polarizer to replace the optical rotation sample. The results show that the new scheme is feasible, this experiment gives the proportion coefficient of the measurement system, the sensitivity of optical rotation measurement increasing up to 3.15× 10^-7 rad, and the measurement precision exceeding 0.3%. Therefore, in this scheme achieved is a high sensitive and precise measurement of optical rotation, and it is expected to be applied to the high sensitive and precise rotation measurement. The verification test experiment designed by us can also provide a outstanding calibration reference for high sensitive rotation measurement system.